Re: [PATCH] staging: android: ashmem: lseek failed due to no FMODE_LSEEK.

[Greg Hackmann]

On 04/06/2017 10:08 AM, Greg KH wrote:
> On Thu, Apr 06, 2017 at 08:30:40AM -0700, Greg Hackmann wrote:
> > On 04/06/2017 07:30 AM, zhangshuxiaomi@xxxxxxxxx wrote:
> > > From: zhangshuxiao <zhangshuxiao@xxxxxxxxxx>
> > >
> > > vfs_llseek will check whether the file mode has
> > > FMODE_LSEEK, no return failure. But ashmem can be
> > > lseek, so add FMODE_LSEEK to ashmem file.
> > >
> > > Signed-off-by: Shuxiao Zhang <zhangshuxiao@xxxxxxxxxx>
> > > Tested-by: Greg Hackmann <ghackmann@xxxxxxxxxx>
> > > ---
> > >  drivers/staging/android/ashmem.c | 1 +
> > >  1 file changed, 1 insertion(+)
> > >
> > > diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
> > > index 3f11332..e4530ac 100644
> > > --- a/drivers/staging/android/ashmem.c
> > > +++ b/drivers/staging/android/ashmem.c
> > > @@ -392,6 +392,7 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma)
> > >  			ret = PTR_ERR(vmfile);
> > >  			goto out;
> > >  		}
> > > +		vmfile->f_mode |= FMODE_LSEEK;
> > >  		asma->file = vmfile;
> > >  	}
> > >  	get_file(asma->file);
> >
> > This commit message is missing some important context.
> >
> > ashmem_llseek() passes the llseek() call through to the backing shmem file.
> > 91360b02ab48 ("ashmem: use vfs_llseek()") changed this from directly calling
> > the file's llseek() op into a VFS layer call.  This also adds a check for
> > the FMODE_LSEEK bit, so without that bit ashmem_llseek() now always fails
> > with -ESPIPE.
> >
> > I've tested that this patch fixes the regression on both hikey running AOSP
> > and User Mode Linux running Debian.
>
> Thanks for letting me know, I'll update the changelog a bit.  How far
> back does this patch need to go in stable kernel releases?
>
> thanks,
>
> greg k-h

3.18 and later.